Recording body for electrostatic recording



CHARGE ACCEPTING LAYER PAPER BASE SUPPORT F|G.3

CONDUCTIVE LAYER PLASTIC FILM FIG-4 Feb. 3, 1970 KIY OSHI TAKAGI ETAL 3,493,427

- RECORDING BODY FOR ELECTROSTATIC RECORDING Filed July 2, 1954 CHARGE ACCEPTING LAYER v CONDUCTIVE LAYER w F|G F|G 5A ANTI- RL LAYER CHA ACCEPTING LAYER IIIIIIII 3 2 I'll I CONDUCTIVE LAYER United States Patent 3,493,427 RECQRDING BODY FOR ELECTROSTATIC RECORDING Kiyoshi Takagi and Kunihiko Tasai, Kawasaki-ski, and Kenmi Tsukataui, Mitaka-shi, Japan, assiguors to Fujitsu Limited, Kawasaki, Japan, a corporation of Japan Filed July 2, 1964, Ser. No. 379,974 Claims priority, application Japan, July 6, 1963, 38/35,806 Int. Cl. B44d 1/18 U.S. Cl. 117201 5 Claims ABSTRACT OF THE DISCLOSURE Described is a sheaf for multiple recording of electrostatic recording by an electrode. The sheaf consists of a plurality of layered sheets. Each sheet consists of a charge accepting layer and at least one other layer. The charge accepting layer has a surface conductivity in the range to 10 'y. The at least one other layer is a conductive layer and has a volume conductivity in the range 1() to l0- 'y/cm.

This invention relates to electrostatic recording, and more particularly to methods and means for obtaining multiple copies from a single exposure to the original.

Electrostatic recording or copying is based on the principle of using a film or sheet bearing a film that accepts an electrostatic charge, electrostatically charging local areas of this film corresponding to the image being recorded, developing the image by means of a recording medium or toner that is electrostatically attracted to the charged areas and fixing the developed image, usually by fusing the toner to the film.

The electrostatic charges characteristically accumulate at the exposed surfaces of the film or paper bearing the film. For this reason, it is relatively simple to obtain good images on the exposed surface of the film. However, it is difficult to obtain multiple copies by a single exposure.

According to the known principles of electrostatic printing or xerography, the sheet material that is to receive the imprint consists of a dielectric material having high specific resistance, for example polystyrene. The sheet may consist entirely of this high resistance material or it may be a composite of a thin film of the high resistance material on a base of a more substantial nature for physical support.

For producing a print, the recording sheet (usually a composite) is placed between two electrodes of which one, called the pattern electrode, has a front face consisting of the type or pattern to be reproduced, and the other electrode being merely an oppositely charged electrode. A high voltage is then impressed between the two electrodes to produce an electrostatic field on the recording sheet. While this field is generated, the electrodes or the sheet may be moved relative to each other to expose the entire sheet. The electrostatic field imposes a charge upon the dielectric surface of the sheet corresponding to the charge configuration on the pattern electrode. Thus, the electrostatic latent image of the pattern is reproduced with an electric polarity and charge density depending upon the applied voltage.

Thereafter, the sheet is removed from between the electrodes and subjected to a developing and fixing process which converts the latent electrostatic image to a visible permanent one. This is accomplished by contacting the sheet surface with powdered dielectric toner material that electrostatically adheres only to the charged areas on the exposed film. The toner is then fixed in place by chemical means or by fusion, depending upon the nature of the toner material.

Variations of the above general principle have been adapted to convert and transfer images by optical, electronic and other means to electrostatic images which are rendered permanent and visible and being all substantially in accordance with the general principles employed in xerography.

The recording or reproducing method of this type produces only one copy at a time. When several sheets of the type normally used in xerography are assembled into a composite, and attempts are made to simultaneously impress an electrostatic latent image and then develop and fix the image, the resultant duplicate images are nonexistent or so poor as to be virtually non-existent.

When a plurality of sheets are placed upon each other and simultaneously charged by the electrostatic field, the act of separating the sheets from each other is sufiicient to discharge most of any latent electrostatic image thereon. Further, the two charged images on each side of each sheet and on facing sides of adjacent sheets have mutually opposed electric polarities. These tend to interfere with and cancel each other to cause partial or substantially complete neutralization of the image. When such a sheaf of recording sheets (a plural layer composite of recording sheets) is separated and developed, the above-mentioned electric charge troubles and discharge phenomena combine to destroy the latent image and virtually nothing is developed when the toner is applied and fixed.

In US. application Ser. No. 338,345, filed in the United States on Jan. 17, 1964 now Patent No. 3,354,464, of which some of us are the inventors, there is described one method of impressing latent images on a plurality of sheets in a sheaf wherein the image-receiving layer is of high resistance and is distinguished by a controlled surface irregularity. Such surface irregularities appear to affect the receiving layer in a manner permitting retention of the images after the sheets in the sheaf are separated.

It is an object of this invention to provide composite sheaves of sheets of recording paper for simultaneously impressing electrostatic images on all of the sheets in the sheaf. It is another object to provide such sheaves having individual sheets of a nature that they retain the electrostatic images after the sheaves are separated into sheets to permit developing and fixing of permanent visual images.

This invention is based on the principle of providing sheets that are composites made up of at least two layers, one of which is the image-retaining layer and is characterized by a specific conductivity in the range 10- to 1O 'y/cm. and another layer having a specific volume conductivity in the range 1O to lO- y/cmfi and with a preferred surface conductivity in the range 10" to 10" 'y. Other layers may be included in these composite recording sheets. These sheets are assembled into sheaves which are then exposed to the electrostatic image-forming process, separated, developed individually and fixed according to the general terms of xerography.

The invention will be more fully described with reference to the drawings, in which:

FIG. 1 shows schematically and in section a portion of one type of sheet material prepared for use in sheaves according to this invention.

FIG. 2 is a section through another type of sheet according to this invention.

FIGS. 3 and 4 are sections through other sheets showing the layered structures for carrying out this invention.

FIG. 5A is a schematic section of one apparatus for generating electrostatic images in a sheaf of recording sheets.

FIG. 5B is another view of the apparatus of FIG. 5A.

FIGS. 6, 7A and 7B are schematic sections of other specialized apparatus for generating electrostatic images in sheaves according to this invention, and

FIG. 8 similarly is a view of another specialized imagegenerating device.

Referring now specifically to FIG. 1, it is a multilayered composite 5 consisting of a base layer 1 for providing physical support made either of paper or resin film, a relatively conductive layer 2, an image-receiving or charge-accepting layer 3, and a special layer 4 to prevent curling of the composite 5. The base layer 1 as well as curl layer 4 should have volume conductivities within the range 10- tol' 'y/cm. Conductive layer 2 should also lie within this range but most preferably within the range 10* to l0 'y/cm. The surface conductivity of this layer should lie within the narrower range 10- to lO 'y.

We have found that when the volume conductivity of the support, conductive and anti-curl layers 1, 2 and 4 is greater than about lO 'y/crn. these layers will begin to shield the charge-accepting layers of the sheets that lie below them in the sheaf. This value appears to be a relative limit for acceptable conductivity for such layers. When the conductivity in layers 1, 2 and 4 is less than about 10* 'y/cm. it is found that the defects of the conventional sheets, such as cancelling of the charge on the charge-accepting layer 3 and the discharge of the charge-accepting layer 3, as set forth above, begin to be encountered.

The resins used for preparing image-accepting layer 3 have a specific surface conductivity in the range l0 to 10- Image-accepting layer 3 should have a thickness in the range 1 to 10 microns. The volume conductivity of layer 3, after it is formed in situ, may be in the range 10 to 10 'y/cm. but its surface conductivity should be in the range 10 to 10- When the surface conductivity is in the range set forth above, the electrostatic charges which form the image will remain in place and not leak off. Within this range, and in conjunction with the other layer mentioned above, the charges due to friction, which would tend to discharge the image at the time of layer separation, do not build up. Similarly, within this range the electrostatic charge is not high enough to attract dirt or an excess build-up of toner during the development process.

Referring now specifically to FIG. 2, this is a multilayer composite 25 consisting of a conductive support 21 and a charge-accepting layer 3 deposited thereon. Support layer 21 which is made of paper or film, prepared in the manner as will be presently set forth to have a conductivity within the range of the conductive layer, serves two purposes, i.e., that of physical support and providing conductivity adjacent to the charge-accepting layer 3. Support layer 21 must, to be most effective, have a conductivity within the ranges set forth for the conductive layer element 2 of the previous figure.

Referring now specifically to FIG. 3, it represents a composite consisting of a support layer 1, a conductive layer 2 on one side of support 1 and a charge-accepting layer 3 on the opposite side of support layer 1. The conductance values of the individual layers are as set forth above.

FIG. 4 shows an alternate method of preparing a composite 45 for constructing the sheaves upon which this invention is based. It consists of a self-supporting film 43 of to microns thickness as a self-supporting charge-accepting layer and conductive film 6- deposited on one side of charge-accepting layer 43. Conductive layer 6 should have its specific conductance in the preferred range 10- to IO- 'y/cm. and should have a surface conductivity in the range 10" to 10* 'y. By virtue of this process, the entire composite 45 can consequently be made much thinner, thereby permitting more leaves per sheaf to have images impressed thereon in conventional apparatus in the course of the practice of this invention.

The conductive layers 2 and 6 and the conductivity of support layers 1 and 21, as well as anti-curl layer 4, are controlled within the limits set forth by any of the five general methods listed below or their equivalents.

(1) The layers may consist of water-soluble resins in which are dispersed organic and inorganic salts in quantities sufficient to achieve the desired and preferred conductivities. Such water-soluble resins include polyvinyl alcohol, methyl cellulose, polyacrylic acid sodium salt, natural gums such as Gum Arabic, etc. Salts useful for modifying the conductivity include LiCl, NaNO Na.COO.CH etc., and are added to the resin solutions in measured amounts.

(2) Organic resins dissolved in ionic or in non-ionic solvents containing polar surface-active agents which are charge-preventing. Among such resins are polystyrol, polymethylmethacrylate, polycarbonates, polyvinyl ohl0- ride, polyvinylacetal and polyvinyl acetate.

(3) The more porous support bases can have their conductivity controlled within the desired limits by impregnation with a charge-preventing solvent (a proprietary material of this sort is available under the trade name Colcote and is sold by the Japan Colcote Com- P y)- (4) The paper support or films may include conductive substances such as finely divided ZnO, ZnS, Cu O, CdS, CdSe. The papers may be treated with slurries of such suspensions and films may have such powders diffused therethrough during casting.

(5) The same limits of specific conductivity can also be achieved by a vacuum deposition of a layer of semiconductive or conductive material such as, for example, CdS, ZnS, Ge, Si, Zn, Ag, etc. The layers are adjusted to the desired conductivity range by controlling the thickness of the film of material being deposited or by the physical characteristics of combinations of materials be ing deposited.

The charge-accepting or image-forming layer is prepared by using any of the film-forming polymeric resins art-recognized for this purpose. Included among such film-forming image-accepting layer materials are polystyrene, polycarbonate, polymethylmethacrylate, polyvinyl chloride, polyvinylacetal, polyvinyl acetate, polyethylene, polypropylene, polytetrafluorethylene, polyethylene terephthalate, cellulose acetate, cellulose polyacetate, ethyl cellulose, and polyisobutylene.

Films of these materials may be prepared, in the known manner, usually by dissolving in a solvent and applying by a coater. However, they may also be deposited from aqueous emulsions or solvent dispersions of solutions or slurries of such resins. Similarly, they may also be directly cast from the molten state onto the support ma terial.

The anti-curl layer 4 is made of conventional polymers commonly used for such purposes, including polyvinyl alcohol, polymethylmethacrylate, methylmethacrylate and polyvinyl acetate. These are usually applied in layers 3 to 8 microns in thickness. In the practice of this invention such special purpose layers are suitably modified with respect to specific conductivity by the use of any of the five expedients set forth above.

The sheaves for receiving the electrostatic images for multiple development are prepared by assembling the requisite number of sheets, all similarly oriented with respect to their charge-accepting layers and lightly compressing them. Two to five of such sheets are adequate for most purposes, but more may also be used if the dimensional capacity of the machine with regard to physical clearances as well as the electrical capacity i.e. charge intensity, is adequate. When the signal voltage is applied, an electrostatic image is formed on each of the sheets. Upon removal from the image-forming area, the sheaves are separated and the individual sheets are developed in the conventional manner by use of toner powder and then they are fixed by fusion of the tone. The voltages applied in the image-forming step vary with the total sheaf assembly. The exposure time may vary and to some extent will permit of variation of the voltage for a given thickness. By way of example, 1800 volts are required for a sheaf according to this invention consisting of three sheets each, 30 microns thick. At such a voltage, the time may range from 1 to 100 microseconds.

The individual sheets need not be restricted to use in sheaves. They can also be used individually to yield excellent xerographic copies. However, in such cases, due to the possibility of the shock of the corona streamer upon the image-receiving layer, care should be taken to suitably adjust the electrode clearances and the applied voltage needed for multiple copies to limit the corona effect within the capabilities of the single sheets.

The actual formation of the images according to the process aspects of this invention, will be demonstrated with respect to the drawings, particularly FIGS. 5, 6, 7 and 8, where FIGS. SA and 5B show that the sheaf of recording sheets 555 is passed through the gap between pattern electrode 52 containing the image-forming charge and ground electrode 53. The roller-type configuration of electrode 52 and the image-forming charges 54 thereon can be seen in FIG. 5B. The sheaf of recording sheets 555 moves between the electrodes and at the same time electrode 52 slowly rotates and imparts its configured electrostatic charge onto the sheaf 555.

FIG. 6 is a variation wherein the pattern electrode 62, the image-forming electrode, and the ground electrode 63 are stationary, and the sheaf 555 moves therebetween. The variations in the image are obtained by variations in the electrostatic charge upon electrode 62. Alternately, electrode 62 may receive its configured charge at another position and then imparts this chargre onto the moving sheaf when it is in opposition to electrode 63.

FIG. 7A shows the use of a pin-matrix electrode 72 in opposition to ground electrode 73. Sheaf 555 moves therebetween. The image is generated by variation of the charges at the individual pin positions of the pin-matrix electrode 72. FIG. 7B shows a typical configuration of such a pin-matrix electrode which may be activated by an electronic read out apparatus to give specific configurations to the image.

FIG. 8 shows a different system adapted for facsimile recording. Here the sheaf 555 is wound around ground electrode 83 and an electrostatic charge is imparted by point electrode 82. Point electrode 82 horizontally scans the rotating sheaf mounted on ground electrode 83. The timing of the electrostatic discharge from point electrode 82 forms the individual images on the charge-accepting layers of recording sheets contained in sheaf 555.

The invention will be more fully described and explained with respect to the following examples wherein are described specific formulations for formation of the various layers comprising the recording sheets which are then collated into sheaves.

EXAMPLE 1 Paper support sheets of the type normally used in xerozgraphic recording were impregnated with an aqueous solution containing 5% polyvinyl alcohol and 0.5% LiCl. One side of each sheet was then coated with a polycarbonate resin xerographic recording layer. The final thickness of each sheet was 38 microns. The specific volume conductivity of the impregnated paper base was 10" 'y/cm. The surface conductivity was 10- '7. Four such sheets were assembled and the assembled sheaf was inserted between the letter and counter electrodes of a xerographic machine. A latent electrostatic image was formed on all four layered sheets by the application of a 2400 v. potential between the letter and counter electrodes. The sheets in this stack were separated and developed in a toner bath of colored resin powder. The

developed image was fixed by the application of heat to yield sharp, clear images on each sheet from the exposed sheaf.

EXAMPLE 2 Volume Surface conductivity conductivity Sheet position /cmJ) (7) Top 10 10 Bottom 10- 10-" Intermediate a 10-" 1O These support sheets were then coated on one face with a 5 micron layer of polycarbonate charge-accepting material. The sheets were collated into a sheaf in the order indicated, exposed at 3500 volts to a pin-matrix electrode for 20 microseconds. The sheaf was then separated, powder-developed and fixed. Good clear images of equal intensities were obtained from each layer of the sheaf.

EXAMPLE 3 A suspension containing 50 parts by weight of zinc oxide in parts by weight of a 5% aqueous solution of polyvinyl alcohol was applied to a film of polyethylene terephthalate 6 microns thick. The resultant sheet was 15 microns thick. The volume conductivity of the applied layer was 10* 'y/cm. A sheaf consisting of three such film sheets was exposed between an image and counter electrode by a 200 volt pulse lasting 20 microseconds. The sheaf was separated and the sheets were developed and fixed in the usual manner. The images on each polyethylene terephthalate film sheet were clean, clear and of equal density.

We claim.

1. A sheaf for the multiple recording of electrostatic recording by an electrode, consisting of a plurality of layered sheets, each sheet consisting of a charge accepting layer and at least one conductive layer, said charge accepting layer having a surface conductivity in the range 10- to 10 'y, and said conductive layer having volume conductivity in the range 10- to l0 /cm.

2. The sheaf according to claim 1, wherein at least one conductive layer of the sheet comprises a conductive compound dispersed in a polymeric matrix.

3. The sheaf according to claim 2, wherein the conductive compound is chosen from the group consisting of conductive inorganic salts and metal oxides.

4. The sheaf according to claim 2, wherein the polymeric matrix is a water-soluble resin chosen from the group consisting a polyvinyl alcohol, polyacrylic acid sodium salt, methyl cellulose, and film-forming natural gums.

5. An electrostatically imprintable sheet member for use in sheaves consisting of a plurality of such members for multiple electrostatic printing, said sheet consisting of an image-accepting layer having a surface conductance in the range 10 to 10 'y and other more conductive layers, each of said other layers having volume conductivities in the range 10' to 'y/cm.

(References on following page) References Cited UNITED STATES PATENTS Ivatts 33--137 La Pierre 346136 Rackett 156-64 Moodie et a1. 34683 Middleton et a1. 117-64 Middleton 117-34 X Silvernail et a1 117201 8 FOREIGN PATENTS 639,318 4/1962 Canada.

FOBERT F. BURNETT, Primafy Examiner 5 W. A. POWELL, Assistant Examiner US. Cl. X.R. 

